Photodielectric effect in thin-film structures of the poly[NiSalen] metallopolymer

This paper reports on the results of investigations of the temperature-frequency dispersion and the kinetics of photodielectric response in metallopolymer structures containing divalent nickel, which have been prepared through electrochemical polymerization. It has been demonstrated that the photodielectric effect observed in the samples under investigation is integral in character due to photoconduction stimulated by light-induced transitions of electrons to the antibonding orbital in the system of π-bonds of the polymer and owing to additional polarization of the nitrogen-containing coordination site of the monomer.     

Frequency dispersion of the dielectric characteristics in polymer films based on the [NiSalen] complex

The results of the measurements of the dielectric properties exhibited by metal-containing polymer structures based on Ni(II) complexes in the frequency range f = 10²–10⁵ Hz are reported. It is established that, in the range of acoustic frequencies, the permittivity ε decreases with increasing frequency, whereas the dielectric loss tangent tan δ increases. At frequencies f > 10⁴ Hz, the dependence tan δ(f) is characterized by a relaxation maximum. The possible mechanisms of dielectric polarization and charge transfer in an alternating-current electric field are considered.     

Specific features of photo-and electrical conduction in manganese germanium garnets

The specific features of photo-and electrical conduction in manganese germanium garnet crystals are investigated in the temperature range 4.2–370 K for the first time. Under exposure of samples with ohmic contacts to visible light, the photocurrent in these samples is observed only at high temperatures. The characteristic times of the photocurrent rise differ from those of photocurrent relaxation after the light is switched off. The inference is made that the photo-and electrical conduction is determined by the electrical recharging of manganese ions. The generation and transport of charge carriers are controlled by centers with electrical inhomogeneities and shallow attachment levels.     

Specific features in the synthesis, crystal structure and electrical conductivity of BICUTIVOX

The formation of solid solutions Bi₄V_2 − xCu_x/2Ti_x/2O_11 − x (0.025 ≤ x ≤ 0.5) known as BICUTIVOX, synthesized by three different methods (a conventional solid-state synthesis, solid-state synthesis enhanced by mechanical activation, and through liquid precursors), has been studied. Based on crystal structure investigations carried out at different temperatures, ranges of stability and temperatures of phase transitions for different polymorphous modifications have been defined. The morphology and the local chemical composition of the ceramic samples obtained have been studied. Thermal expansion coefficients have been measured. The electrical conductivity of ceramic samples has been investigated in a wide range of temperatures and partial oxygen pressures.     

Specific features of oxygen-ionic conduction in oxide nanoceramics

The effect of surface tension on the activation energy for oxygen-ionic conduction in nanoceramics is considered. The activation energy is calculated for oxygen ion diffusion through oxygen vacancies, which are treated as dilatation centers. The activation energy is shown to decrease as the nanoparticle size decreases. Based on the size distribution function of nanoparticles, the activation energy distribution function is calculated. Analytical expressions are obtained for the dependences of the ionic conduction on temperature and nanoparticle size. The increase of two to three orders of magnitude in the oxygen-ionic conduction observed earlier in the ZrO₂: 16% Y nanoceramics is adequately described by these expressions. The surface tension of nanoparticles is shown to cause a substantial increase in the oxygen-ionic conduction observed in nanoceramics; the main contribution to the conductivity is related to a region near the particle surface.     

Specific features of hopping conduction in bismuth-containing oxide layered ceramics

The dynamic conduction of bismuth-containing oxide layered ceramics of the composition Sr₂Bi₂TiNb₂O₁₂ is investigated in a weak alternating field at frequencies of 0.5–500 kHz in the temperature range 300–700 K. It is demonstrated that the high-temperature conduction can be adequately described in terms of theoretical concepts using the effective medium method and corresponds to two-dimensional hopping transfer. The concentration of nodes in the system through which charge-carrier hopping occurs is estimated.     

Specific features of the electrical conductivity of V6O11

A study has been made of the electrical conductivity of V₆O₁₁ single crystals over a broad range of temperatures covering the regions of the metal phase, metal-insulator phase transition, and insulator phase. It has been shown that the electrical conductivity of the metal phase correlates with the Mott limit of minimum conductivity. To explain the temperature dependence of the electrical conductivity of the V₆O₁₁ insulator phase, the theory of hopping conduction taking into account the effect of thermal vibration of atoms on the resonance integral has been invoked.     

Defect structure and electrical conduction behavior of Bi-based pyrochlores

Pyrochlore-type quaternary systems with the generic formula (Bi_1.5Zn_0.5)(Nb_0.5M_1.5)O₇ (BZNM, M=Ti, Sn, Zr, and Ce) have been synthesized by the standard solid-state reaction route. The study of positron annihilation lifetime spectra provides direct evidence for defect characterization for BZNM ceramics with different tetravalent element. The variation of the annihilation lifetime suggests that the defect structure undergoes significant changes. The defect structure is further described by means of the complex-defect model. Electrical conduction in the samples is expected to result mainly from the defects present in the lattice. Conduction measurement shows there are different conduction mechanisms. For temperatures less than 350 °C, electronic conduction dominates, while for temperatures greater than 350 °C, ionic conduction is dominant in the present system. The conduction mechanism includes the formation of charged defect dipoles, causing internal bias fields, creating oxygen vacancies that promote ionic conductivity.     

Optical and electrical conduction mechanisms of [N(CH3)3H]CdCl3

The X-ray powder diffraction patterns shows that at room temperature [N(CH₃)₃H]CdCl₃ crystallizes in the orthorhombic system with the Pbnm space group. The analysis of the data revealed the existence of optical allowed direct transition mechanisms with the band gap energy equal to 5.3 eV. The temperature dependences of the real part of dielectric permittivity show a relaxation process at high temperature that can be explained by the reorientational motion of alkyl chains. The alternative current (AC) electrical conduction in compound is governed by three processes, which can be attributed to several models: the correlated barrier hopping (CBH) model in phases I and II, the non-overlapping small polaron tunneling (NSPT) model in phases III and IV.     

Specific features of the CuI nanocrystal structure in photochromic glasses

Physics of the Solid State - The absorption spectra of CuI nanocrystals with an average radii of 5.3 and 6.2 nm in photochromic glass matrix have been studied in the temperature range 38–300...     

Specific features of the space-time structure of acoustic signals in multimode waveguides

The effect of the diffraction focusing of an acoustic field on the space-time intensity distribution of narrow-band pulsed signals in multimode oceanic waveguides is analytically and numerically studied. The laws governing this effect and its specific features are illustrated by the results of calculations based on the standard ray approximation and the mode theory for the acoustic field in an isovelocity waveguide.     

Specific features of the temperature characteristics of electrical conductivity and photoconductivity of polymer composites containing Cu(II)/Cr(III) heterometallic complexes

The temperature characteristics of the electric current and the photocurrent in films of composites based on electrically neutral poly(vinyl butyral) with additions of Cu(II)/Cr(III) heterometallic cation-anion complexes are investigated. The electrical conductivity and photoconductivity of the polymer composite films in the visible optical range increase with a decrease in the distance between the metal centers in the complexes and upon introduction of acceptor additions of the C₆₀ fullerene into the composition of the polymer binder and increase exponentially with increasing temperature. The activation energy of electrical conduction and photoconduction exceeds 1 eV and depends weakly on the strength of the external electric field. The temperature characteristics of the electrical conductivity and photoconductivity of the materials under investigation are explained by the specific features of trapping of charge carriers at the interface between particles of the heterometallic complex and the polymer binder.     

Specific features of electrical conductivity of the insulating phase of vanadium dioxide doped with niobium

The electrical conductivity of V_{1 – x}Nb_xO₂ single crystals have been investigated over a wide temperature range covering regions of the existence of the metallic and insulating phases. It has been shown that, with an increase in the niobium concentration, the electrical conductivity of the metallic phase becomes below the Mott limit for the minimum metallic conductivity. Immediately after the metal–insulator transition, the electrical conductivity is determined by a large amount of free electrons that gradually localized with a decrease in the temperature. The temperature dependence of the electrical conductivity in the insulating phase of V_{1 – x}Nb_xO₂ has been explained in the framework of the hopping conductivity model that takes into account the effect of thermal vibrations of atoms on the resonance integral.     

Specific features of speckle structure formed by dispersed laser beams

The geometry of statistical average of intensity speckles formed by a broadband dispersed laser beam spatially coherent in initial plane z = 0 is studied theoretically. A computer simulation was used to obtain two-dimensional distributions of random intensity that provide a clear picture of the transformations experienced by the speckle structure upon laser beam propagation. Correlation functions and power spectra of random intensity are calculated in order to determine the characteristic size and shape of speckles as a function of longitudinal coordinate z, the width and shape of the frequency spectrum, and the degree of dispersion of the light beam. Analytical expressions that describe an increase in the speckle size along the beam axis and in the direction of beam dispersion as a function of distance from the initial plane are obtained. The ultimate (at z → ∞) width of speckles in the direction of beam dispersion is calculated.     

Specific features of the structure of semiconducting sms polycrystals in the homogeneity region

The structure and thermal properties of polycrystalline samples of samarium monosulfide have been investigated in the homogeneity region (Sm_{1 + x} S at 0 < x < 0.17). The X-ray structural parameters and porosity of the samples have been measured, and their correlation with the thermodynamic parameters of the first-order phase transition occurring in polycrystalline samarium monosulfide at temperatures in the range from 240 to 260 K in Sm_{1 + x} S has been established. It has been assumed that the measured nanopores correspond to voids between misoriented coherent X-ray scattering regions. It has been shown that the maximum of the absorbed heat energy is achieved in the case where the volume of the pore becomes comparable to the volume of the nucleus of a new phase of samarium sulfide, which is calculated from thermodynamic relationships.     

Electro-optic polymer ring resonator modulators [Invited]

Electro-optic(EO) ring resonator modulators have a number of communications and scientific applications, including analog optical links, optical signal processing, and frequency comb generation. Among the EO materials used to fabricate ring modulators, the EO polymer has many promising characteristics, including a high EO coefficient of 100–200 pm/V(3–7 times larger than that of Li Nb O3), an ultrafast EO response time( 10 fs), a low dielectric constant(3 to 4) with very little dispersion up to at least 250 GHz, and a straightforward spin-coating fabrication process. These inherent characteristics will be able to combine excellent EO properties with simple processing in achieving exceptional performance in a variety of high-speed optical modulation and sensing devices. This review focuses on the research and recent development of ring resonator modulators based on EO polymers. The first part describes the operation principle of EO ring resonator modulators, such as modulation mechanism, EO tunability, and 3 d B bandwidth. Subsequently, the emphasis is placed on the discussion of the ring modulators with EO polymers as the waveguide core and the improvement of EO modulation by using an EO polymer/titanium dioxide hybrid core. At the end, a series of EO polymers on silicon platforms including slot modulators, etching-free modulators, and athermal modulators are reviewed.     

Specific features in the behavior of electrical resistivity of the pine biocarbon preform/copper composite

The electrical resistivity ρ(T) of the novel type of composites prepared by infiltrating melted copper in vacuum in empty sap channels of white pine high-porosity biocarbon preforms has been measured in the temperature range 5–300 K. Biocarbon preforms have been prepared by pyrolysis of tree wood in an argon flow at two carbonization temperatures, 1000 and 2400°C. The electrical resistivity of the composites has been found to vary relatively weakly with temperature and to pass through a characteristic minimum near 40–50 K, which can be ascribed to iron and manganese impurities penetrating into copper from the carbon preform when liquid copper is infiltrated into it. It has been shown that the electrical resistivity ρ(T) of the composites is governed primarily by the specific microstructure of the preform, which is made up of parallel channels with an average diameter of about 50 μm interrupted by systems of thin capillaries. The small cross section of the copper-filled capillaries accounts for these regions providing the major contribution to the electrical resistivity of the composites. An increase in the wood carbonization temperature brings about a noticeable increase in the effective capillary cross section and a decrease in the electrical resistivity ρ(T) of the composite.